Wafer probing test has been an important step for ensuring that the semiconductor devices manufactured on a wafer are not defective before they are packaged. A conventional automatic wafer probing system (AWPS) as shown in FIG. 1 consists of a platen 1, a forcer 2 on which a wafer chuck 3 is mounted, a ring carrier 4 on which a microscope 5 is mounted, a CCD camera 6 for pattern recognition, a wafer Z-profile sensing assembly 7, and a material handling assembly, which is not shown in the figure, for loading and unloading a wafer for testing. In general, an X-Y coordinate system is assumed on the platen 1 and the forcer 2 can do positional translation on it, either in X, Y, or simultaneously X and Y directions. The wafer chuck 3 can move in Z (height) direction as well as perform a .theta. rotation. In addition to holding a probe card in place, the ring carrier 4 has a few precision alignment posts for level-adjusting the probe card by the operator during an initial setup time. Because the AWPS has an automatic alignment module working associated with the CCD camera for doing pattern recognition, the coordinate of the wafer under test can easily be figured out.
FIG. 2 shows a conventional Epoxy needle probe card that is usually used to test one single die during each test. Since the needle type test pins are long, they induce parasitic induction and capacitance effects. Therefore, impedance match becomes difficult to accomplish and causes the degradation of the test speed. In addition, the X-Y shift at the contact test point as well as the difficulty in meeting the area-array pins are some drawbacks of such a probe card. Although needle type probe cards have been built for testing multiple dies, these cards having a large number of pins are expensive to build, maintain and repair. Besides, it is very time consuming to repair damages of such cards and the repairing can only be done by a skilled operator.
As integrated circuits become faster and more complex, the number of input/output (I/O) pads increases drastically. In order to accommodate the increasing number of I/O pads, the size and spacing of pads must decrease. I/O pads in an area-array format have been proposed for integrated circuits having large number of inputs and outputs. For circuit chips designed to be used in multi-chip modules (MCM), the area-array format becomes more common and may replace the traditional periphery format. The probing test of such chips using conventional needle probe cards, however, is very difficult because of the area-array format and the reduction in pad size and spacing.
The traditional approach of using a conventional probe card to interface a chip introduces parasitic capacitance and inductance that make it impossible to test the chip at full speed. Therefore, chips that are functional but do not meet speed requirements are usually packaged and then scraped later. This has become a severe problem as the operational speed of circuit devices continues to increase. Scraping and reworking finished systems that do not meet speed requirements greatly increases manufacturing cost. Therefore, it has become essential to test circuit devices such as MCMs at fill speed. Furthermore, the output drivers of an advanced circuit device are designed with a smaller size in anticipation of reduced parasitic effects between chips. Hence, they are less effective in driving the conventional probe card and the tester. An accurate sort of good chips at the wafer level can save significant packaging costs. In order to provide a better screening process at the wafer level, it is necessary to use probe cards that have higher resolutions and allow testing at higher speeds. The probe cards also have to place less loading to the output drivers of the device under test.
An electronic membrane prober is a membrane style probe card fabricated from a silicon wafer with typical integrated circuit and micro-machining technologies. The membrane prober (MP) is capable of providing a very large number of probe tips in any format, including area-array prober pad format, and is designed to satisfy the requirements of high speed and high resolution wafer-level testing. The membrane is a thin, free-handling and low stress layer of silicon, silicon dioxide, silicon carbide, silicon nitride or polyimide. FIG. 3 shows a conceptual design of the membrane prober. The probe lines are aluminum and the probe tips are tungsten. The probe card is fabricated with conventional integrated circuit processing techniques that are well established. In addition, more functionality can be added to the prober because active test circuitry can also be placed on the membrane prober.
The membrane film of a membrane prober provides the mechanical support for the probe lines and tips as well as the alignment of the probe card to the wafer under test if the membrane film is transparent. Although there are many advantages over a conventional epoxy needle probe card, it is necessary that the membrane prober has the transparency characteristic on its membrane film. When the density of the test tips and the area of the membrane become higher and larger, the transparency requirement will be difficult to meet. It may be possible to design a sophisticated optical system between the membrane prober and the wafer under test so that they can be aligned. However, the cost and maintenance are expensive. In addition, the space constraint on a wafer probing test system may make the manipulation of such a complex optical alignment system unappreciative.